Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$34.66	10.105%	$38.1624	$38.16	$38.15	$38.20
Purchase #2	$131.43	10.728%	$145.5298	$145.53	$145.55	$145.50
Purchase #3	$215.41	7.841%	$232.3003	$232.30	$232.30	$232.30
Purchase #4	$178.81	6.308%	$190.0893	$190.09	$190.10	$190.10
Purchase #5	$234.43	12.465%	$263.6517	$263.65	$263.65	$263.70
Purchase #6	$53.35	12.202%	$59.8598	$59.86	$59.85	$59.90
Purchase #7	$17.78	4.706%	$18.6167	$18.62	$18.60	$18.60
7 purchase totals =	$865.87		$948.2100	$948.21	$948.20	$948.30